The Collegiate Church of Saint Peter and Alexander (Stiftsbasilika) is the oldest significant building in Aschaffenburg, with foundations going back to the 10th century. The building as it stands today is a Romanesque structure substantially reworked over centuries, with additions ranging from a Gothic cloister to Renaissance details. The whole ensemble backs up against the hillside in the old town, creating a striking silhouette from the river.
Inside, the church contains an impressive collection of works accumulated over centuries, including Romanesque stone relief sculptures, a carved altarpiece, and most notably a Lamentation panel by Matthias Grünewald. The Romanesque cloister attached to the church is one of the better-preserved examples in the region and is a peaceful spot to sit. The church is usually open during the day and free to enter.